45
the resulting materials, allow the easy entry of water molecules to the polymer
matrix, thus destroying the pyridinium ring-PU H-bond interactions, as a result, the
Tg is reduced. Zhang’s research group also reported the water-induced shape memory phenomenon from crosslinked PVA hydrogels, thus obtaining materials that can
recorver their original shape after 45 min at room temperature (Du and Zhang 2010).
3.4.2.4 Electrical and Magnetic Induced SMPUs
Electrical and magnetic SMPs are indirect thermo-responsive SMPs. The electroand magneto-type SMPs are constructed from conductive or magnetic materials
such as conductive carbon black, metal powders, conductive polymers and
ferromagnetic inorganic particles. The composite materials increase the temperature of the system by electric current or the heat generated by the alternating magnetic field (AMF), which leads to the shape recovery. Therefore, composite materials
possess electrical conductivity, magnetic responsiveness and excellent shape memory function (Cai et al. 2013a, b; Gong et al. 2012; Niu and Cohn 2013; Razzaq
et al. 2007b; Zhang et al. 2013). Compared to traditional thermo-sensitive SMPs,
composite materials could be continuously heated by electric and magnetic fields,
which is of great value to design complex devices and realize localized heating
(Razzaq et al. 2007a; Weigel et al. 2009; Xiao et al. 2010; Yu et al. 2009). For example, Xiao et al. (2010) obtained shape memory composite materials from crosslinked PCL and carbon nanotubes by the application of a DC alternating electric
field. These authors obtained a sperial-shape material as the initial shape and after
the application of an DC alternating electric field for 22 s, the material had a
straight shape.
Today, most of the developed SMPs studied are stimulated by direct contact
stimuli. However, non-contact stimulation methods, such as AMF, electric field,
infrared light, laser and ultrasound can be safely used for medical applications.
3.4.2.5 Applications of SMPUs
Based on the above research process, SMPUs could be applied in many fields due
to the advantage of permeability, mechanical properties and temperature
adjustability.
Until now, SMPUs are mainly used for textile applications, as breathability and
water resistance can effectively improve shape memory performance. Keeping this
in mind, Mondal and Hu (2007) investigated the water vapor permeability of SMPUcoated textiles, noting that SMPUs can be adjusted with body temperature. However,
SMPUs generally cannot tightly control shape memory performance for different
practical applications because the recovery temperature is not accurate enough.
In addition, the excellent mechanical properties, high blood compatibility and
temperature adjustability from SMPUs broaden the prospects of SMPUs for medical applications. The biodegradability of the PU materials could be imparted by
using biodegradable polymers as the soft segment, while the Tg of the PUs could be
3 Smart and Shape Memory Polymers
the resulting materials, allow the easy entry of water molecules to the polymer
matrix, thus destroying the pyridinium ring-PU H-bond interactions, as a result, the
Tg is reduced. Zhang’s research group also reported the water-induced shape memory phenomenon from crosslinked PVA hydrogels, thus obtaining materials that can
recorver their original shape after 45 min at room temperature (Du and Zhang 2010).
3.4.2.4 Electrical and Magnetic Induced SMPUs
Electrical and magnetic SMPs are indirect thermo-responsive SMPs. The electroand magneto-type SMPs are constructed from conductive or magnetic materials
such as conductive carbon black, metal powders, conductive polymers and
ferromagnetic inorganic particles. The composite materials increase the temperature of the system by electric current or the heat generated by the alternating magnetic field (AMF), which leads to the shape recovery. Therefore, composite materials
possess electrical conductivity, magnetic responsiveness and excellent shape memory function (Cai et al. 2013a, b; Gong et al. 2012; Niu and Cohn 2013; Razzaq
et al. 2007b; Zhang et al. 2013). Compared to traditional thermo-sensitive SMPs,
composite materials could be continuously heated by electric and magnetic fields,
which is of great value to design complex devices and realize localized heating
(Razzaq et al. 2007a; Weigel et al. 2009; Xiao et al. 2010; Yu et al. 2009). For example, Xiao et al. (2010) obtained shape memory composite materials from crosslinked PCL and carbon nanotubes by the application of a DC alternating electric
field. These authors obtained a sperial-shape material as the initial shape and after
the application of an DC alternating electric field for 22 s, the material had a
straight shape.
Today, most of the developed SMPs studied are stimulated by direct contact
stimuli. However, non-contact stimulation methods, such as AMF, electric field,
infrared light, laser and ultrasound can be safely used for medical applications.
3.4.2.5 Applications of SMPUs
Based on the above research process, SMPUs could be applied in many fields due
to the advantage of permeability, mechanical properties and temperature
adjustability.
Until now, SMPUs are mainly used for textile applications, as breathability and
water resistance can effectively improve shape memory performance. Keeping this
in mind, Mondal and Hu (2007) investigated the water vapor permeability of SMPUcoated textiles, noting that SMPUs can be adjusted with body temperature. However,
SMPUs generally cannot tightly control shape memory performance for different
practical applications because the recovery temperature is not accurate enough.
In addition, the excellent mechanical properties, high blood compatibility and
temperature adjustability from SMPUs broaden the prospects of SMPUs for medical applications. The biodegradability of the PU materials could be imparted by
using biodegradable polymers as the soft segment, while the Tg of the PUs could be
3 Smart and Shape Memory Polymers